Infrared absorption filter

ABSTRACT

The infrared absorption filter of the present invention has a transmittance of not higher than 30% in the near-infrared region in the wavelength range of 800 to 1100 nm; a difference of 10% or less between a maximum value and a minimum value of transmittance in the visible light region in the wavelength range of 450 to 650 nm; and a transmittance of not lower than 50% at a wavelength of 550 nm, the filter being so excellent in environmental stability that after being left to stand in the air atmosphere at a temperature of 60° C. and a humidity of 95% for 1000 hours, the filter can maintain said spectral property in said range. Consequently, when used for a plasma display or the like, the filter can absorb the unwanted infrared rays radiated from the display, resulting in preventing erroneous operation of a remote control using infrared radiation even in such a high-temperature and high-humidity environment. The filter is gray in color so that when placed in front of a display, the color originated in the display can be seen without discoloration.

CROSS REFERENCE TO RELATED APPLICATION

More than one reissue application has been filed for the reissue of U.S.Pat. No. 6,522,463. The reissue applications are application Ser. No.10/897,394, and its continuation, application Ser. No. 10/897,393 (thepresent application).

FIELD OF THE INVENTION

The present invention relates to an optical fiber, and more particularlyto an optical filter which has a high transmittance in the visible lightregion and which is capable of intercepting infrared radiation. Thefilter of the present invention is especially useful for displaypurposes.

BACKGROUND ART

The following filters have been conventionally used as a heatray-absorbing filter or as a filter for adjusting the visibility ofvideo camera:

-   -   (1) a filter composed of phosphate glass containing metallic        ions such as copper or iron ions (Japanese Unexamined Patent        Publication No.235740/1985, Japanese Unexamined Patent        Publication No.153144/1987, etc.);    -   (2) an interference filter having plural layers differing from        each other in refractive index on a substrate to allow light of        specific wavelength to pass by interference of transmitted light        (Japanese Unexamined Patent Publication No.21091/1980, Japanese        Unexamined Patent Publication No.184745/1984, etc.);    -   (3) an acrylic resin filter composed of a copolymer containing        copper ions (Japanese Unexamined Patent Publication        No.324213/1994); and    -   (4) a filter composed of a binder resin and a coloring matter        dispersed in the binder resin (Japanese Unexamined Patent        Publication No.21458/1982, Japanese Unexamined Patent        Publication No.198413/1982, Japanese Unexamined Patent        Publication No.43605/1985, etc.).

The above-mentioned conventional infrared absorption filters haveproblems as described below.

The filter (1) exhibits sharp absorption in the near-infrared region andcan intercept infrared radiation at a very high ratio. However, thefilter (1) pronouncedly absorbs part of red color in the visible lightregion so that the transmitted color looks blue. For display purposes,importance is laid on a color balance. In such case, it is difficult touse the filter (1). Another problem is raised about the processabilityof the filter (1) because it is made of glass.

The optical properties of the filter (2) can be freely designed. Furthera filter having properties almost equal to the designed properties canbe produced. However, the filter (2) necessitates a plurality of layersdiffering in refractive index from each other for this purpose,consequently entailing a drawback of incurring high production costs.Moreover, when a large area is required, the filter (2) should have auniform thickness of high precision over the entire area, resulting in adifficulty in producing the filter.

The filter (3) has improved processability compared with the filter (1).However, the filter (3) exhibits sharp absorption and absorbs the redcolor of light beams as is the case with the filter (1), raising thesame problem as the filter (1) that the filter (3) looks blue.

In the filter (4), various infrared-absorbing materials can be used.Examples of useful materials are phthalocyanine, nickel complex, azocompound polymethine, diphenylmethane, triphenylmethane, quinone and thelike. However, when singly used, these materials pose problems ofshowing insufficient absorption or absorbing a visible light of specificwavelength in the visible light region. Further, when the filter is leftto stand at a high temperature or a high humidity for a long time, theinfrared-absorbing materials involve problems of decomposing oroxidizing, bringing about absorption in the visible light region orceasing absorption in the infrared region.

An object of the present invention is to provide an infrared absorptionfilter which can achieve absorption in the near-infrared region, thefilter showing a high transmittance in the visible light region, beingfree from marked absorption of a light of specific wavelength in thevisible light region, and being excellent in environmental stability andin processability and productivity.

DISCLOSURE OF THE INVENTION

The present invention was completed in view of the foregoing situation.The infrared absorption filters of the present invention which haveovercome the above-mentioned problems are as described below.

The first invention provides an infrared-absorbing filter which has atransmittance of not higher than 30% in the near-infrared region in thewavelength range of 800 to 1100 nm; a difference of 10% or less betweena maximum value and a minimum value,of transmittance in the visiblelight region in the wavelength range of 450 to 650 nm; and atransmittance of not lower than 50% at a wavelength of 550 nm,

said filter, after being left to stand in the air atmosphere of atemperature of 60° C. and a humidity of 95% for 1000 hours, having atransmittance of not higher than 30% in the near-infrared region in thewavelength range of 800 to 1100 nm, and a difference of 10% or lessbetween a maximum value and a minimum value of transmittance in thevisible light region in the wavelength range of 450 to 650 nm.

The second invention provides an infrared absorption filter as definedin the first invention, wherein after being left to stand in the airatmosphere of a temperature of 80° C. for 1000 hours, the filter has atransmittance of not higher than 30% in the near-infrared region in thewavelength range of 800 to 1100 nm and has a difference of 10% or lessbetween a maximum value and a minimum value of transmittance in thevisible light region in the wavelength range of 450 to 650 nm.

The third invention provides an infrared absorption filter as defined inthe first invention, wherein the filter has an infrared-absorption layeron a transparent substrate, the layer being composed of a coloringmatter, dye or pigment for absorbing infrared radiation and a polymerserving as a dispersing medium.

The 4th invention provides an infrared absorption filter as defined inthe third invention, wherein the amount of the solvent remaining in theinfrared-absorbing layer is 5.0 wt. % or less.

The 5th invention provides an infrared absorption filter as defined inthe third invention, wherein the transparent substrate has a total lighttransmittance of not lower than 89%, a haze of not higher than 1.6%, acoefficient of static friction of not higher than 0.6 and a coefficientof dynamic friction of not higher than 0.6.

The 6th invention provides an infrared absorption filter as defined inthe third invention, wherein the transparent substrate is a polyesterfilm.

The 7th invention provides an infrared absorption filter as defined inthe third invention, wherein the polymer constituting theinfrared-absorption layer has a glass transition temperature of notlower than 80° C.

The 8th invention provides an infrared absorption filter as defined inthe 7th invention, wherein the polymer constituting theinfrared-absorbing layer is a polyester resin.

The 9th invention provides an infrared absorption filter as defined inthe third invention, wherein the filter has an electroconductive layerof metal mesh having an aperture ratio of not less than 50% on the sameside as the infrared-absorbing layer of the filter or on the opposedside thereof.

The 10th invention provides an infrared absorption filter as defined inthe third invention, wherein the filter has a transparentelectroconductive layer on the same side as the infrared-absorbing layerof the filter or on the opposed side thereof.

The 11th invention provides an infrared absorption filter as defined inthe 10th invention, wherein the transparent electroconductive layer isformed of a metal oxide.

The 12th invention provides an infrared absorption filter as defined inthe 10th invention, wherein the transparent electroconductive layer hasa repeatedly laminated structure in which at least three layers arelaminated in the order of metal oxide/metal/metal oxide.

The 13th invention provides an infrared absorption filter as defined inthe 12th invention, wherein the constituent metal layer of thetransparent electroconductive layer is formed of silver, gold, or acompound containing any of them.

The 14th invention provides an infrared absorption filter as defined inthe first invention, wherein a hard coat-treated layer is formed as anoutermost layer of the filter.

The 15th invention provides an infrared absorption filter as defined inthe first invention, wherein an antireflection layer is formed as anoutermost layer of the filter.

The 16th invention provides an infrared absorption filter as defined inthe first invention, wherein an antiglare-treated layer is formed as anoutermost layer of the filter.

The 17th invention provides an infrared absorption filter as defined inthe first invention, wherein the filter is disposed in front of a plasmadisplay.

The infrared absorption filter of the present invention is required tohave a transmittance of not higher than 30% in the near-infrared regionin the wavelength range of 800 to 1100 nm. Since the infrared absorptionfilter of the present invention has a low transmittance in this region,the filter used for a plasma display or the like can absorb the unwantedinfrared radiation emitted from the display, thereby making it possibleto prevent erroneous operation of a remote control using infraredradiation.

The infrared absorption filter of the present invention essentially hasa difference of 10% or less between a maximum value and a minimum valueof transmittance in the visible light region in the wavelength range of450 to 650 nm. When the infrared absorption filter of the presentinvention has the difference in this range of transmittance within thewavelength range of 450 to 650 nm, the filter is given a gray color, andthe color originating from the display can be seen withoutdiscoloration.

Further, the infrared absorption filter of the present inventionessentially has a transmittance of not lower than 50% at a wavelength of550 nm. If the transmittance is lower than 50% at said wavelength, thedisplay looks very dark when the filter is placed in front of thedisplay.

After being left to stand in the air atmosphere at a temperature of 60°C. and a humidity of 95% for 1000 hours, the infrared absorption filterof the invention essentially has a transmittance of not higher than 30%in the near-infrared region in the wavelength range of 800 to 1100 nmand a difference of 10% or less is found between a maximum value and aminimum value of transmittance in the visible light region in thewavelength range of 450 to 650 nm.

After being left to stand in the air atmosphere at a temperature of 80°C. for 1000 hours, the infrared absorption filter of the inventionpreferably has a transmittance of not higher than 30% in thenear-infrared region in the wavelength range of 800 to 1100 nm and adifference of 10% or less is recognized between a maximum value and aminimum value of transmittance in the visible light region in thewavelength range of 450 to 650 nm.

Embodiments of the present invention are described below in detail.

According to a preferred embodiment of the invention, an infraredabsorption filter is prepared by dispersing an infrared-absorbingmaterial(s) in a polymer and coating a transparent substrate with theobtained dispersion. This process simplifies the production and enablessmall-lot production.

Preferably the amount of residual solvent(s) in a coating layer of theinfrared absorption filter is 5.0 wt. % or less, the filter beingprepared by depositing a composition on a substrate, the compositionbeing prepared by dispersing in a binder resin a near-infrared-absorbingmaterial(s) containing a diimmonium salt compound represented by theformula (1)

wherein R₁-R₈ are the same or different from each other and eachrepresents hydrogen or alkyl having 1 to 12 carbon atoms, and Xrepresents SbF₆, ClO₄, PF₆, NO₃ or halogen.

If the filter containing more than 5.0 wt. % of the solvent in thecoating layer is left to stand at a high temperature and a high humidityfor a long time, the diimmonium salt compound undergoes chemical changeand absorption decreases in the near-infrared region, resulting ininsufficient interception of near-infrared radiation. In this case,absorption increases in the visible light region, leading todiscoloration of the filter in its entirety to deep yellowish green.

To bring the amount of residual solvent(s) to 5.0 wt. % or less, thedrying conditions of the following equations (2) to (4) should besimultaneously fulfilled. The factors in the equation (2) are expressedin the units described blow below: the wind velocity in m/sec, hot airtemperature in °C., drying time in minute minutes and thickness ofcoating layer in μm.Wind velocity×(hot air temperature−20)×drying time/thickness of coatinglayer>48  (2)Hot air temperature:≧80°C.  (3)Drying time:≧ ≦60 minutes  (4)

Binder resins for use herein are not limited insofar as they canuniformly disperse the near-infrared-absorbing material used in theinvention. Suitable examples include, for example, polyester resins,acrylic resins, polyamide resins polyurethane resins, polyolefin resins,polycarbonate resins and the like. Desirably the binder resin fordispersing the near-infrared-absorbing material(s) has a glasstransition temperature which is not less than the assumed guaranteedtemperature for use of the filter of the invention. Thereby thestability of the near-infrared-absorbing material is increased. Theassumed guaranteed temperature for use of the filter of the invention ispreferably 80° C. or higher, more preferably 85° C. or higher.

Solvents useful in preparing a coating solution in the coating processcan be any solvent insofar as they can uniformly disperse thenear-infrared-absorbing material and the binder for use herein. Examplesof useful solvents are acetone, methyl ethyl ketone, methyl isobutylketone, ethyl acetate, propyl acetate, methanol, ethanol, isopropylalcohol, ethyl cellosolve, benzene, toluene, xylene, tetrahydrofuran,n-hexane, n-heptane, methylene chloride, chloroform,N,N-dimethylformamide, water and the like to which the solvents for useherein are not limited.

There is not limitation on infrared-absorbing materials useful in thepresent invention. Examples are as follows.

As the near infrared-absorbing materials, in addition to the diimmoniumsalt compound of the formula (1), one or both of fluorine-containingphthalocyanine compound and dithiol metal complex compound canpreferably be contained in the coating solution. The coating solutionpreferably contains at least two species of diimmonium salt compound,fluorine-containing phthalocyanine compound and nickel complex compound.Preferred proportions of the near infrared-absorbing materials are 0.5to 0.01 parts by weight of fluorine-containing phthalocyanine compoundif used and 1 to 0 part by weight of nickel complex compound, per partby weight of the diimmonium salt compound.

Examples of the diimmonium salt compound of the formula (1) are N,N,N′,N′-tetrakis(p-di-n-butylaminophenyl)-p-benzoquinone-diimmonium.ditetrafluoroantimonate,N,N,N′,N′-tetrakis(p-diethylaminophenyl)-p-benzoquinone-diimmonium.ditetrafluoroantimonate,N,N,N′,N′-tetrakis(p-di-n-butylaminophenyl)-p-benzoquinone-diimmonium.diperchlorate,N,N,N′,N′-tetrakis(p-diethylaminophenyl)-p-benzoquinone-diimmonium.diperchlorate,N,N,N′,N′-tetrakis(p-diisopropylaminophenyl)-p-benzoquinone-diimmonium.ditetrafluorophosphate,N,N,N′,N′-tetrakis(p-n-propylaminophenyl)-p-benzoquinone-diimmonium.dinitrateand so on to which, however, useful diimmonium salt compounds are notlimited. Some of them are commercially available. Among them, KayasorbIRG-022, IRG-023 and the like (products of NIPPON KAYAKU Co., Ltd.) aresuitably usable.

Useful fluorine-containing phthalocyanine compounds include, forexample, Excolor IR1, IR2, IR3 and IR4 (products of NIPPON SHOKUBAI Co.,Ltd.). Useful dithiol metal complex compounds include, for example,SIR-128, SIR-130, SIR-132 and SIR-159 (products of Mitsui Chemicals,Inc.).

The infrared absorption filter of the present invention preferablycontains a UV-absorbing agent to enhance the resistance to light.Furthermore, in the present invention, the polymer for dispersing theinfrared-absorbing material may be crosslinked with a crosslinking agentto impart weather-ability and resistance to solvents to the filter.

There is no limitation on transparent substrate films for use in theinfrared absorption filter of the present invention. Useful transparentsubstrate films include, for example, stretched films formed ofpolyester resins, acrylic resins, cellulose resins, polyethylene resins,polypropylene resins, polyolefin resins, polyvinyl chloride resins,polycarbonate, phenolic resins, urethane resins or the like. From thestandpoint of dispersion stability, environmental load and the like,polyester films are preferable.

In the infrared absorption filter having the infrared-absorbing layer onat least one side of the transparent polymer film, the transparentpolymer film preferably has a total light transmittance of not lowerthan 89%, a haze of not higher than 1.6%, a coefficient of staticfriction of not higher than 0.6 and a coefficient of dynamic friction ofnot higher than 0.6.

The infrared absorption filter of the invention which is often used fordisplay purposes has desirably a high total light transmittance, anddesirably a low haze. However, if inert particles capable of impartingan uneven surface to the film are used in a reduced amount to increasethe total light transmittance and to reduce the haze, generally thecoefficient of friction is increased and the slidability isdeteriorated, making it difficult to carry out the winding or likeoperation. If the total light transmittance, haze and coefficient offriction are within the ranges of the invention, it is possible to bringboth the windability and the total light transmittance to the desiredranges.

In order to give the total light transmittance, haze and coefficient offriction in the above mentioned ranges, it is desirable to form acoating layer of 30 to 300 μm nm thickness on the substrate polymerfilm, the coating layer containing inert particles of small averageparticle size not higher than the wavelength of visible light and not toincorporate inert particles into the substrate polymer film.

Examples of such inert particles are calcium carbonate, calciumphosphate, silica, kaolin, talc, titanium dioxide, alumina, bariumsulfate, calcium fluoride, lithium fluoride, zeolite, molybdenum sulfideand like inorganic particles, crosslinked polymer particles, calciumoxalate and like organic particles. Among them, silica particles are themost suitable because they have a refractive index relatively similar tothat of polyester resin and facilitates formation of a highlytransparent film.

The inert particles to be incorporated into the coating layer have anaverage particle size of preferably 0.01 to 1.0 μm, more preferably 0.02to 0.5 μm, most preferably 0.03 to 0.3 μm. If the average particle sizeof inert particles is greater than 1.0 μm, reduced transparency of thefilm tends to result, whereas the average particle size of less than0.01 μm tends to deteriorate the handleability (slidability,windability, blocking prevention, etc.) of the film. The amount of inertparticles to be incorporated into the coating layer is 0.1 to 60 wt. %,preferably 0.5 to 50 wt. %, more preferably 1.0 to 40 wt. %, based onthe amount of solid in an adhesive layer. If the amount of inertparticles in the coating layer exceeds 60 wt. %, it is likely to impairthe adhesive property of the film and to deteriorate the transparency ofthe film, whereas less than 0.1 wt. % is likely to deteriorate thehandleability (slidability, windability, blocking prevention, etc.) ofthe film.

The filter of the invention preferably has a transparentelectroconductive layer or an electroconductive layer of metal meshhaving an aperture ration of not less than 50% on the same side as theinfrared-absorbing layer of the filter or on the opposed side thereof.Thereby detrimental electromagnetic waves emitted from a display can beremoved.

Metal meshes useful in the present invention include, for example, metalfoils of high electroconductivity treated by etching to give a mesh,fabric meshes produced from metallic fibers, meshes produced, e.g. byplating a metal on the surface of polymeric fibers, etc. Metals to beused for the electromagnetic wave-absorbing layer are not Limited andcan be any metal insofar as the metal is excellent in theelectroconductivity and in stability. However, copper, nickel, tungstenand the like are preferred from the viewpoints of processability andcosts.

The transparent electroconductive layer to be formed in the presentinvention can be any electroconductive layer, but is preferably oneformed from a metal oxide which enables attaining a higher visible lighttransmission. To increase the electroconductivity of the transparentelectroconductive layer, it is preferred to provide a repeatedlylaminated structure in which at least three layers are laminated in theorder of metal oxide/metal/metal oxide. The multilayered metal structureprovides the layer with the desired electroconductivity while retainingthe high visible light transmission.

Metal oxides for use in the invention can be any metal oxide insofar asthey have the desired electroconductivity and visible lighttransmission. Useful metal oxides include, for example, tin oxide,indium oxide, indium tin oxide, zinc oxide, titanium oxide, bismuthoxide, etc. to which useful metal oxides are not limited. The metallayers to be employed in the invention are preferably those formed ofgold, silver or compounds containing any of them from the viewpoint ofelectroconductivity.

When the electroconductive layer has a multi-layered structure, e.g., athree-layer structure comprising layers each formed of metal oxide,metal and metal oxide, respectively in this order, the thickness ofsilver layer is preferably 50 to 200 Å, more preferably 50 to 100 Å. Ifthe silver layer has a thickness exceeding 200 Å, the light transmissionis reduced, whereas less than 50 Å increases the resistance value. Thethickness of metal oxide layer is preferably 100 to 1000 Å, morepreferably 100 to 500 Å. If the thickness of metal oxide layer isgreater than 1000 Å, coloration occurs, resulting in discoloration,whereas less than 100 Å thickness increases the resistance value. When astructure of more than three layers is provided, e.g., a 5-layeredstructure composed of metal oxide, silver, metal oxide, silver and metaloxide in this order, the thickness of intermediate metal oxide layer ispreferably greater than the other metal oxide layers. This increases thelight transmission throughout the multilayered structure.

A hard coat-treated layer (HC) may be formed as an outermost layer toprevent marring on the infrared absorption filter of the invention. Thehard coat-treated layer (HC) may be desirably a cured layer ofcrosslinkable resin, such as polyester resin, urethane resin, acrylicresin, melamine resin, epoxy resin, silicone resin, polyimide resin orthe like which may be used alone or in admixture.

The hard coat-treated layer (HC) has a thickness of preferably 1 to 50μm, more preferably 2 to 30 μm. The thickness of less than 1 μm, thehard coat-treated layer fails to sufficiently achieve the intendedfunction, whereas the thickness of more than 50 μm retards theresin-coating operation, making it difficult to obtain a good resultconcerning the productivity.

The hard coat-treated layer (HC) can be formed on the surface of theside opposed to the side of the transparent electroconductive film, bycoating said surface with the above-mentioned resin by gravure process,reverse process, dyeing process or the like, followed by application ofheat, ultraviolet rays, electron rays or like energy to cure thedeposited resin.

The infrared absorption filter of the invention may contain anantiglare-treated layer (AG) as an outermost layer to enhance thevisibility when used for display purposes.

The antiglare-treated layer (AG) can be formed by coating the surface tobe treated with a curable resin, drying the layer, giving an unevensurface by an embossing roll, and applying heat, ultraviolet rays,electron rays or like energy to cure the deposited resin. Useful curableresins are, for example, polyester resins, urethane resins, acrylicresins, melamine resins, epoxy resins, silicone resins, polyimide resinsand the like which may be used alone or in admixture.

The infrared absorption filter of the invention may contain anantiflection-treated layer (AR) as an outermost layer to enhance thevisible light transmission when used for display purposes. Theantiflection-treated layer (AR) may be desirably a single layer orplural layers of a material(s) which is different in refractive indexfrom the plastic film. The single layer structure is preferably composedof a material which is lower in refractive index than the plastic film.To form a multilayered structure, recommendably the material for thelayer adjacent to the plastic film has a higher refractive index thanthe plastic film and the material for the layer or layers over the saidadjacent layer has a lower refractive index than the adjacent layer.Materials for forming the antireflection-treated layer (AR) are notlimited and may be either organic or inorganic insofar as they canfulfill said relationship of refractive index. Preferred materials aredielectric materials such as CaF₂, MgF₂, NaAlF₄, SiO₂, ThF₄, Nd₂O₃,SnO₂, TiO₂, CeO₂, ZnS, In₂O₃, etc.

The antireflection-treated layer (AR) can be produced by a dry coatingprocess such as vacuum deposition process, sputtering process, CVDprocess, ion plating process or the like or a wet coating process suchas gravure process, reverse process, dyeing process or the like.

Prior to formation of the hard coat-treated layer (HC),antiglare-treated layer (AG) or antireflection-treated layer (AR),various pretreatments may be carried out, which include, for example,conventional treatments such as corona discharge treatment, plasmatreatment, sputtering treatment, electron beam irradiation treatment, UVirradiation treatment, primer treatment, adhesivity-increasing treatmentand the like.

Examples of Embodiments

The present invention will be described in more detail with reference tothe following Examples to which, however, the invention is not limited.Given below are methods of measuring the property values used herein andmethods of evaluating the effect.

(1) Spectral Property

The spectral property was measured with a self-recordingspectrophotometer (Hitachi U-3500 model) in the wavelength range of 1500to 200 nm.

(2) Environmental Stability

1) Moisture Resistance

After the sample was left to stand in the atmosphere of a temperature of60° C. and a humidity of 95% for 1000 hours, the above-mentionedspectral property was measured.

2) Heat Resistance

After the sample was left to stand in the air atmosphere at 80° C. for1000 hours, the above-mentioned spectral property was measured.

(3) Amount of Solvent(s) Remaining in the Coating Layer

The amount of residual solvent(s) was measured using GC-9A (manufacturedby Shimadzu Corp.) as follows. About 5 mg of the sample was preciselyweighted out and was trapped with heating to 150° C. at an inlet port ofa gas chromatograph for 5 minutes. Then the total amount (A: ppm) oftoluene, tetrahydrofuran (THF) and methyl ethyl ketone (MEK) wasmeasured. Since the peaks of THF and MEK overlap each other, they werecompared with the reference peak (toluene) and the combined value wasdetermined as conversion value to toluene. Aside from the above, a pieceof 10 cm square was cut off from the sample and was weighed out (B: g)and the coating layer was wiped with the solvents. The difference (C: g)between the weights of the sample before and after wiping wasdetermined. The amount of residual solvents was calculated by thefollowing equation.The amount of residual solvents (%)=A×B×10⁻⁴/C(4) Total Light Transmittance and Haze

Measured with a haze meter (product of Tokyo Denshoku Kogyo K.K., ModelTC-H3DP) according to JIS K 7105

(5) Coefficient of Friction

The coefficient of static friction (μs) and the coefficient of dynamicfriction (μd) were obtained according to JIS K 7125.

EXAMPLE 1

A base polyester to be used as a dispersing medium was prepared asfollows. Charged into an autoclave equipped with a thermometer and astirrer were:

Dimethyl terephthalate 136 wt. Parts Dimethyl isophthalate 58 wt. PartsEthylene glycol 96 wt. parts Tricyclodecane dimethanol 137 wt. partsAntimony trioxide 0.09 wt. part

These ingredients were heated to 170 to 220° C. for 180 minutes toundergo an ester exchange reaction. Then the temperature of the reactionsystem was elevated to 245° C. to continue the reaction under a pressureof 1 to 10 mmHg for 180 minutes, giving a polyester copolymer resin(A1). The polyester copolymer resin (A1) had an inherent viscosity of0.4 dl/g and a glass transition temperature of 90° C. NMR analysis gavethe following copolymer composition ratio:

Acid components Terephthalic acid 71 mol % Isophthalic acid 29 mol %Alcohol components Ethylene glycol 28 mol % Tricyclodecane dimethanol 72mol %

A flask was charged with the infrared-absorbing materials, theabove-obtained resin and the solvents shown in Table 1 in theproportions indicated therein. The mixture was heated with stirring todissolve the infrared-absorbing materials and the binder resin in thesolvents. The resin solution was applied to a highly transparentpolyester film substrate of 100 μm thickness having a slidable surfaceon one side and a smooth surface on the other side (product of ToyoBoseki K.K., “Cosmoshine A 4100; total light transmittance 90.9%, haze0.7, coefficient of static friction (slidable surface/smooth surface:0.58/>1), coefficient of dynamic friction (slidable surface/smoothsurface: 0.42/>1)) using an applicator with a gap of 100 μm. Thedeposited layer was dried at a wind velocity of 0.4 m/s and atemperature of 90° C. in a hot air drier for 1 hour. The resultingcoating film had a thickness of 25 μm.

The obtained infrared absorption filter had a color of dark gray whenseen. The spectral property qf the filter is shown in FIG. 1. As shownin FIG. 1, the absorption was plotted as flat in the visible lightregion in the wavelength range of 400 to 650 nm. A difference was 4.8%between a maximum value and a minimum value of transmittance in thewavelength range of 450 to 650 nm, and the transmittance in thewavelength range was 69.4% at lowest. The sharp absorption was observedin the wavelength range of 700 nm or higher. The transmittance was 23.4%at highest in the wavelength range of 800 to 1100 nm.

The obtained filter was left to stand in the atmosphere of a temperatureof 60° C. and a humidity of 95% for 1000 hours, and the spectralproperty was evaluated again with the results shown in FIG. 2. While aslight color change occurred, a difference of 9.8% was found between amaximum value and a minimum value of transmittance in the wavelengthrange of 450 to 650 nm and the transmittance in the wavelength range was65.5% at lowest. The transmittance was 29.1% at highest in thewavelength range of 800 to 1100 nm and the filter retained thenear-infrared-absorbing property.

Further, the obtained filter was left to stand in the atmosphere of atemperature of 80° C. for 1000 hours, and the spectral property wasevaluated again with the results shown in FIG. 3. While a slight colorchange was brought about, a difference was 5.8% between a maximum valueand a minimum value of transmittance in the wavelength range of 450 to650 nm and the transmittance in the wavelength range was 67.2% atlowest. The transmittance was 21.0% at highest in the wavelength rangeof 800 to 1100 nm and the filter retained the near-infrared-absorbingproperty.

When disposed in front of a plasma display or the like, the obtainedfilter showed no change of color and increased the contrast, resultingin reduced level of near-infrared radiation.

TABLE 1 Ingredient Material Amount Near- Diimmonium salt compound, 3.2wt. Parts infrared- Kyasorb IRG-022 manufactured absorbing by NipponKayaku Co., Ltd. material Fluorine-containing 0.5 wt. Partphthalocyanine compound, Excolor IR-1 manufactured by Nippon ShokubaiCo., Ltd. Dithiol metal complex 1.6 wt. Parts compound, SIR-159manufactured by Mitsui Chemicals, Inc. Binder resin Polyester copolymerresin 440 wt. Parts (A1) Solvent Methyl ethyl ketone 490 wt. PartsTetrahydrofuran 490 wt. Parts Toluene 490 wt. Parts

Comparative Example 1

Vylon RV 200 manufactured by Toyo Boseki K.K., (specific weight 1.26,glass transition temp. 67° C.) was used as a base polymer. A flask wascharged with the infrared-absorbing materials, the binder resin and thesolvents as shown in Table 2 in the proportions indicated therein. Theseingredients were heated with stirring to dissolve the theinfrared-absorbing materials and the binder resin in the solvents. Theresin solution was applied to a highly transparent polyester filmsubstrate of 100 μm thickness (product of Toyo Boseki K.K., “CosmoshineA 4100”) using an applicator with a gap of 100 μm. The deposited layerwas dried at a wind velocity of 0.4 m/s and a temperature of 90° C. in ahot air drier for 1 hour. The resulting coating film had a thickness of25 μm. The obtained infrared absorption filter had a brown color whenseen. As shown by the spectral property of the filter in FIG. 4, theabsorption was plotted in a mountain-shaped form having a peak at about550 nm in the visible light region in the wavelength range of 400 to 650nm. A difference was 11.5% between a maximum value and a minimum valueof transmittance in the wavelength range of 450 to 650 nm, and thetransmittance in the wavelength range was 71.4% at lowest. The sharpabsorption was observed in the wavelength range of 700 nm or higher. Thetransmittance was 44.0% at highest in the wavelength range of 800 to1100 nm. The filter looked green when seen. When disposed in front of aplasma display of the like, the obtained filter lost a color balance,and turned greenish.

The obtained filter was left to stand in the atmosphere of a temperatureof 60° C. and a humidity of 95% for 1000 hours, and the spectralproperty was evaluated again with the following results. A differencewas increased from 11.5% to 28.6% between a maximum value and a minimumvalue of transmittance in the wavelength range of 450 to 650 nm and thetransmittance in the wavelength range was 54% at lowest. Thetransmittance was increased to 49.0% at highest in the wavelength rangeof 800 to 1100 nm. The filter was deep green when seen. The spectralproperty is shown in FIG. 5. When disposed in front of a plasma displayor the like, the obtained filter lost a color balance, and turnedgreenish.

Further, the obtained filter was left to stand in the atmosphere of atemperature of 80° C. for 1000 hours, and the spectral property wasevaluated again with the following results. A difference rose from 11.5%to 20.3% between a maximum value and a minimum value of transmittance inthe wavelength range of 450 to 650 nm and the transmittance in thewavelength range was 61.8% at lowest. The transmittance was increased to47.2% at highest in the wavelength range of 800 to 1100 nm. The filterwas deep green when seen. The spectral property of the filter is shownin FIG. 6. When disposed in front of a plasma display or the like, theobtained filter lost a color balance, and turned greenish.

TABLE 2 Ingredient Material Amount Near- Diimmonium salt compound, 3.2wt. parts infrared- Kyasorb IRG-022 manufactured absorbing by NipponKayaku Co., Ltd. material Binder resin Vylon RV 200 manufactured by 440wt. parts Toyo Boseki K.K. Solvent Methyl ethyl ketone 490 wt. partsTetrahydrofuran 490 wt. parts Toluene 490 wt. parts

Comparative Example 2

Vylon RV 200 (product of Toyo Boseki K.K., specific weight 1.26, glasstransition temp. 67° C.) was used as a base polymer. A flask was chargedwith the infrared-absorbing materials, the binder resin and the solventsas shown in Table 3 in the proportions indicated therein. Theseingredients were heated with stirring to dissolve the infrared-absorbingmaterials and the binder resin in the solvents. The resin solution wasapplied to a highly transparent polyester film substrate of 100 μmthickness (product of Toyo Boseki K.K., “Cosmoshine A 4100”) using anapplicator with a gap of 100 μm. The deposited layer was dried at a windvelocity of 0.4 m/s and a temperature of 90° C. in a hot air drier for 1hour. The resulting coating film had a thickness of 25 μm.

The obtained infrared absorption filter was dark gray when seen. Thespectral property of the filter was substantially the same as inExample 1. The absorption was plotted as flat in the visible lightregion in the wavelength range of 400 to 650 nm. The sharp absorptionwas observed at 700 nm or more.

The obtained filter was left to stand in the atmosphere of a temperatureof 60° C. and a humidity of 95% for 1000 hours, and the spectralproperty was evaluated again with the results shown in FIG. 7. Adifference was increased from 4.8% to 27.4% between a maximum value anda minimum value of transmittance in the wavelength range of 450 to 650nm, and the transmittance in the wavelength range was 44.0% at lowest.The transmittance was increased to 47.2% at highest in the wavelengthrange of 800 to 1100 nm. The filter looked green when seen. Whendisposed in front of a plasma display or the like, the obtained filterlost a color balance, and turned greenish.

Further the obtained filter was left to stand in the atmosphere of atemperature of 80° C. for 1000 hours, and the spectral property wasevaluated again with the results shown in FIG. 8. A difference wasincreased from 4.8% to 16.6% between a maximum value and a minimum valueof transmittance in the wavelength range of 450 to 650 nm and thetransmittance in the wavelength range was 56.3% at lowest. Thetransmittance was increased to 30.2% at highest in the wavelength rangeof 800 to 1100 nm. The filter looked green when seen. When disposed infront of a plasma display or the like, the obtained filter looked green.

TABLE 3 Ingredient Material Amount Near- Diimmonium salt compound, 3.2wt. parts infrared- Kyasorb IRG-022 manufactured absorbing by NipponKayaku Co., Ltd. material Fluorine-containing 0.5 wt. partphthalocyanine compound, Excolor IR-1 manufactured by Nippon ShokubaiCo., Ltd. Dithiol metal complex 1.6 wt. parts compound, SIR-159manufactured by Mitsui Chemcials, Inc. Binder resin Vylon RV 200manufactured by 440 wt. parts Toyo Boseki K.K. Solvent Methyl ethylketone 490 wt. parts Tetrahydrofuran 490 wt. parts Toluene 490 wt. parts

EXAMPLE 2

A coating solution was prepared using the polyester copolymer resin (A1)described in Example 1 together with the other ingredients shown inTable 1 in the proportions indicated therein. The coating solution thusobtained was applied to a highly transparent polyester film substrate of100 μm thickness (product of Toyo Boseki K.K., “Cosmoshine A 4300”,total transmittance 90.9%, haze 0.7, coefficient of static friction(both surfaces) 0.58, coefficient of dynamic friction (both surfaces)0.42) by a gravure roll. The deposited layer was dried for 1 minute byfeeding hot air at a wind velocity of 5 m/s and a temperature of 130° C.and then the filter was wound into a roll. The resulting coating layerhad a thickness of 8.0 pm. The amount of residual solvents in thecoating layer was 4.1 wt %. The filter had a high slidability and showeda good roll appearance.

The obtained infrared absorption filter looked dark gray when seen. Thespectral property of the filter is shown in FIG. 9. As shown in FIG. 9,the absorption was plotted as flat in the visible light region in thewavelength range of 400 to 650 nm. The sharp absorption was observed ata wavelength of 700 nm or more.

The obtained filter was left to stand in the atmosphere of a temperatureof 60° C. and a humidity of 95% for 1000 hours, and the spectralproperty was evaluated again with the results shown in FIG. 10. Thefilter showed no great change in the spectral curve and exhibited stableperformance.

Comparative Example 3

The coating solution used in Example 1 was applied to a highlytransparent polyester film substrate (product of Toyo Boseki K.K.,“Cosmoshine A 4300”) by a gravure roll. The deposited layer was driedfor 1 minute by feeding hot air at a wind velocity of 5 m/s and atemperature of 120° C. The coating layer had a thickness of 11 μm. Theamount of residual solvents in the coating layer was 6.5 wt. %. Thefilter looked dark gray when seen. The spectral property of the filteris shown in FIG. 11. As shown in FIG. 11, the absorption was plotted asflat in the visible light region in the wavelength range of 450 to 650nm. The sharp absorption was observed at a wavelength of 700 nm or more.

The obtained filter was left to stand in the atmosphere of a temperatureof 60° C. and a humidity of 95% for 1000 hours, and the spectralproperty was evaluated again with the results shown in FIG. 12. Asindicated in FIG. 12, the absorption in the near-infrared region loweredand the color of the filter turned yellowish green.

EXAMPLE 3

In the transparent polyester film having the infrared-absorbing layer asobtained in Example 2, a hard coat-treated layer (HC) was formed on thesurface of the side opposed to the infrared-absorbing layer. Used as ahard coat material was a UV-curable resin composition comprising 100parts of an epoxy acrylic resin and 4 parts of benzophenone. The hardcoat-treated layer was formed by a bar coat method. Then, preliminarydrying was conducted at 80° C. for 5 minutes and the layer was cured byUV radiation with 500 mJ/cm². The cured hard coat-treated layer (HC) hada thickness of 5 μm.

Copper foil of 9 μm thickness was bonding to the surface ofinfrared-absorbing layer with a UV-curing adhesive, the bonded copperfoil was patterned with photoresist and etched to give a anelectromagnetic wave shielding layer. The copper foil had lines of 15 μmwidth, a pitch of 115 μm and an aperture ration of 75%.

FIG. 13 shows the spectral property of the filter having, as describedabove, the hard coat-treated layer on one side of the transparentpolyester film substrate, and the infrared-absorbing layer and theelectromagnetic wave shielding layer superposed in this order on theother side thereof. As shown in FIG. 13, it was found that the filtercan absorb near-infrared rays, has a gray color and exhibits a highvisible light transmission while absorbing an electromagnetic wave.

The obtained filter was left to stand in the atmosphere of a temperatureof 60° C. and a humidity of 95% for 1000 hours, and the spectralproperty was evaluated again with the following results. Although alittle changed in color, the filter maintained the near-infraredabsorbing property. When disposed in front of a plasma display or thelike, the obtained filter did not undergo change of color and increasedthe contrast, resulting in the decrease in radiation of near-infraredbeams and in radiation of electromagnetic wave.

EXAMPLE 4

In the transparent polyester film having an infrared-absorbing layer asobtained in Example 2, a hard coat-treated layer (HC) was formed on thesurface of the side opposed to the infrared-absorbing layer. Used as ahard coat material was a UV-curing resin composition comprising 100parts of an epoxy acrylic resin and 4 parts of benzophenone. The hardcoat-treated layer was formed by a bar coat method. Then, preliminarydrying was conducted at 80° C. for 5 minutes and the layer was cured byUV radiation with 500 mJ/cm². The cured hard coat-treated layer (HC) hada thickness of 5 μm.

A thin film of tin oxide with 380 Å thickness was formed on theinfrared-absorbing layer by a high-frequency magnetron sputteringdevice. Then a thin film of silver with 200 Å thickness was laminated onsaid thin film by a DC magnetron sputtering device. Further a thin filmof tin oxide with 410 Å thickness was laminated thereon to form aelectromagnetic wave shielding layer. The electromagnetic wave shieldinglayer had a surface resistance value of 4 Ω/□. FIG. 14 shows thespectral property of the filter having, as described above, the hardcoat-treated layer on one side of the transparent polyester filmsubstrate, and the infrared-absorbing layer and the electromagnetic waveshielding layer laminated in this order on the other side thereof. Asshown in FIG. 14, the filter can absorb near-infrared rays, has a graycolor, and exhibits a high visible light transmission while absorbingthe electromagnetic wave.

The obtained filter was left to stand in the atmosphere of a temperatureof 60° C. and a humidity of 95% for 1000 hours, and the spectralproperty was evaluated again with the following results. Although alittle changed in color, the filter maintained the near-infraredabsorbing property. When disposed in front of a plasma display or thelike, the obtained filter did not undergo change of color and increasedthe contrast, resulting in the decrease in radiation of near-infraredbeams and in radiation of electromagnetic wave.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the spectral property of the infrared absorption filterprepared in Example 1.

FIG. 2 shows the spectral property of the infrared absorption filterprepared in Example 1 after the filter was left to stand in theatmosphere of a temperature of 60° C. and a humidity of 95% for 1000hours.

FIG. 3 shows the spectral property of the infrared absorption filterprepared in Example 1 after the filter was left to stand in theatmosphere of a temperature of 80° C. for 1000 hours.

FIG. 4 shows the spectral property of the infrared absorption filterprepared in Comparative Example 1.

FIG. 5 shows the spectral property of the infrared absorption filterprepared in Comparative Example 1 after the filter was left to stand inthe atmosphere of a temperature of 60° C. and a humidity of 95% for 1000hours.

FIG. 6 shows the spectral property of the infrared absorption filterprepared in Comparative Example 1 after the filter was left to stand inthe atmosphere of a temperature of 80° C. for 1000 hours.

FIG. 7 shows the spectral property of the infrared absorption filterprepared in Comparative Example 2 after the filter was left to stand inthe atmosphere of a temperature of 60° C. and a humidity of 95% for 1000hours.

FIG. 8 shows the spectral property of thy infrared absorption filterprepared in Comparative Example 2 after the filter was left to stand inthe atmosphere of a temperature of 80° C. for 1000 hours.

FIG. 9 shows the spectral property of the infrared absorption filterprepared in Example 2.

FIG. 10 shows the spectral property of the infrared absorption filterprepared in Example 2 after the filter was left to stand in theatmosphere of a temperature of 60° C. and a humidity of 95% for 1000hours.

FIG. 11 shows the spectral property of the infrared absorption filterprepared in Comparative Example 3.

FIG. 12 shows the spectral property of the infrared absorption filterprepared in Comparative Example 3 after the filter was left to stand inthe atmosphere of a temperature of 60° C. and a humidity of 95% for 1000hours.

FIG. 13 shows the spectral property of the infrared absorption filterprepared in Example 3.

FIG. 14 shows the spectral property of the infrared absorption filterprepared in Example 4.

EFFECTS OF THE INVENTION

The infrared absorption filter of the present invention has broadabsorption in the near-infrared region, shows a high visible lighttransmission and does not markedly absorb a specific light in thevisible light wavelengths. When used for a plasma display or the like,the filter can absorb the unwanted infrared radiation emitted from thedisplay, thereby making it possible to prevent erroneous operational ofa remote control using infrared radiation. The infrared absorptionfilter of the present invention is gray in color so that it is unlikelyto cause color change when used for a video camera, display or the like.Further the filter of the invention has such a high environmentalstability that the filter can maintain said properties in an environmentof a high temperature and a high humidity.

1. An infrared absorption filter which has a transmittance of not higherthan 30% in the near-infrared region in the wavelength range of 800 to1100 nm; a difference of 10% or less between a maximum value and aminimum value of transmittance in the visible light region in thewavelength range of 450 to 650 nm; and a transmittance of not lower than50% at a wavelength of 550 nm, said filter, after being left to stand inthe air atmosphere at a temperature of 60° C. and a humidity of 95% for1000 hours, having a transmittance of not higher than 30% in thenear-infrared region in the wavelength range of 800 to 1100 nm, and adifference of 10% or less between a maximum value and a minimum value oftransmittance in the visible light region in the wavelength range of 450to 650 nm, said filter having an infrared-absorbing layer on atransparent substrate, the infrared-absorbing layer being composed of acoloring matter, dye or pigment absorbing infrared radiation and apolymer serving as a dispersing medium and the transparent substratehaving a total light transmittance of not lower than 89%, a haze of nothigher than 1.6%, a coefficient of static friction of not higher than0.6 and a coefficient of dynamic friction of not higher than 0.6.
 2. Theinfrared absorption filter according to claim 1, wherein after beingleft to stand in the air atmosphere at a temperature of 80° C. for 1000hours, the filter has a transmittance of not higher than 30% in thenear-infrared region in the wavelength of 800 to 1100 nm and has adifference of 10% or less between a maximum value and a minimum value oftransmittance in the visible light region in the wavelength of 450 to650 nm.
 3. The infrared absorption filter according to claim 1, whereinthe amount of a solvent remaining in the infrared-absorbing layer is 5.0wt % or less.
 4. The infrared absorption filter according to claim 1,wherein the transparent substrate is a polyester film.
 5. The infraredabsorption filter according to claim 1, wherein the polymer constitutingthe infrared-absorbing layer has a glass transition temperature of notlower than 80° C.
 6. The infrared absorption filter according to claim5, wherein the polymer constituting the infrared-absorbing layer is apolyester resin.
 7. The infrared absorption filter according to claim 1,wherein the filter has an electroconductive layer of metal mesh havingan aperture ratio of not less than 50% on the same side as theinfrared-absorbing layer of the filter or on the opposed side thereof.8. The infrared absorption filter according to claim 1, wherein thefilter has a transparent electroconductive layer on the same side as theinfrared-absorbing layer of the filter or on the opposed side thereof.9. The infrared absorption filter according to claim 8, wherein thetransparent electroconductive layer is formed of a metal oxide.
 10. Theinfrared absorption filter according to claim 8, wherein the transparentelectroconductive layer has a repeatedly laminated structure in which atleast three layers are laminated in the order of metal oxide/metal/metaloxide.
 11. The infrared absorption filter according to claim 10, whereinthe constituent metal layer of the transparent electroconductive layeris formed of silver, gold or a compound containing any of them.
 12. Theinfrared absorption filter according to claim 1, wherein a hardcoat-treated layer is formed as an outermost layer of the filter. 13.The infrared absorption filter according to claim 1, wherein anantireflection layer is formed as an outermost layer of the filter. 14.The infrared absorption filter according to claim 1, wherein anantiglare-treated layer is formed as an outermost layer of the filter.15. The infrared absorption filter according to claim 1, wherein thefilter is disposed in front of a plasma display.
 16. An infraredabsorption filter comprising a transparent substrate and aninfrared-absorbing layer formed thereon, the filter being prepared bycoating the transparent substrate with a coating solution comprising aninfrared-absorbing material, a binder resin and a solvent, the binderresin being selected from polyester resins, acrylic resins, polyamideresins, polyurethane resins, polyolefin resins and polycarbonate resins,and the amount of the solvent remaining in the infrared-absorbing layerbeing 5.0 wt. % or less.
 17. The infrared absorption filter according toclaim 16, wherein the binder resin has a glass transition temperature ofnot lower than 80° C.
 18. The infrared absorption filter according toclaim 16, wherein the binder resin is a polyester resin.
 19. Theinfrared absorption filter according to claim 16, wherein the filter hasan electroconductive layer of metal mesh having an aperture ratio of notless than 50% on the same side as the infrared-absorbing layer of thefilter or on the opposed side thereof.
 20. The infrared absorptionfilter according to claim 16, wherein the filter has a transparentelectroconductive layer on the same side as the infrared-absorbing layerof the filter or on the opposed side thereof.
 21. The infraredabsorption filter according to claim 20, wherein the transparentelectroconductive layer is formed of a metal oxide.
 22. The infraredabsorption filter according to claim 20, wherein the transparentelectroconductive layer has a repeatedly laminated structure in which atleast three layers are laminated in the order of metal oxide/metal/metaloxide.
 23. The infrared absorption filter according to claim 22, whereinthe constituent metal layer of the transparent electroconductive layeris formed of silver, gold or a compound containing any of them.
 24. Theinfrared absorption filter according to claim 16, wherein a hardcoat-treated layer is formed as an outermost layer of the filter. 25.The infrared absorption filter according to claim 16, wherein anantireflection layer is formed as an outermost layer of the filter. 26.The infrared absorption filter according to claim 16, wherein anantiglare-treated layer is formed as an outermost layer of the filter.27. The infrared absorption filter according to claim 16, wherein thefilter is disposed in front of a plasma display.
 28. The infraredabsorption filter according to claim 16, wherein the filter has atransmittance of not higher than 30% in the near-infrared region in thewavelength range of 800 to 1100 nm, and after being left to stand in theair atmosphere at a temperature of 60° C. and a humidity of 95% for 1000hours, the filter has a transmittance of not higher than 30% in thenear-infrared region in the wavelength range of 800 to 1100 nm.
 29. Theinfrared absorption filter according to claim 28, wherein the filter hasa difference of 10% or less between the maximum value and the minimumvalue of transmittance in the visible light region in the wavelengthrange of 450 to 650 nm and a transmittance of not lower than 50% at awavelength of 550 nm, and after being left to stand in the airatmosphere at a temperature of 60° C. and a humidity of 95% for 1000hours, the filter has a difference of 10% or less between the maximumvalue and the minimum value of transmittance in the visible light regionin the wavelength range of 450 to 650 nm.
 30. The infrared absorptionfilter according to claim 16, wherein the filter has a transmittance ofnot higher than 30% in the near-infrared region in the wavelength rangeof 800 to 1100 nm, and after being left to stand in the air atmosphereat a temperature of 80° C. for 1000 hours, the filter has atransmittance of not higher than 30% in the near-infrared region in thewavelength range of 800 to 1100 nm.
 31. The infrared absorption filteraccording to claim 30, wherein the filter has a difference of 10% orless between the maximum value and the minimum value of transmittance inthe visible light region in the wavelength range of 450 to 650 nm and atransmittance of not lower than 50% at a wavelength of 550 nm, and afterbeing left to stand in the air atmosphere at a temperature of 80° C. for1000 hours, the filter has a difference of 10% or less between themaximum value and the minimum value or transmittance in the visiblelight region in the wavelength range of 450 to 650 nm.
 32. The infraredabsorption filter according to claim 16, wherein the infrared-absorbingmaterial contains a dimmonium salt compound.
 33. The infrared absorptionfilter according to claim 32, wherein the dimmonium salt compound isrepresented by the formula (1):

wherein R₁ -R ₈ are the same or different from each other and eachrepresents hydrogen or alkyl having 1 to 12 carbon atoms, and Xrepresents SbF ₆ , ClO ₄ , PF ₆ , NO ₃ or halogen.
 34. The infraredabsorption filter according to claim 16, wherein the infrared-absorbingmaterial contains at least two species of dimmonium salt compound,fluorine-containing phthalocyanine compound and nickel complex compound.